The present invention relates to a method and an apparatus for contactless determination of a lateral offset relative to a straight-ahead direction when an object moves relative to an object with a stochastic surface structure, by imaging the surface structure on a photosensor.
Conventionally, for this purpose, a sensor is attached to an object in motion, by means of which measured variables relative to another object with a stochastic surface can be detected. For example, an object in motion can be a vehicle, the movement of which relative to the road surface is detected. Often in such cases, the lateral offset is to be determined as a deviation of the vehicle movement from straight-ahead travel. For as long as the vehicle travels, for example, straight ahead and no disruptive influences act on the vehicle, no lateral offset can be detected. It is conceivable that, for example, a side wind gust impinging upon a vehicle moving straight ahead displaces the vehicle laterally.
The invention relates particularly to a method and an apparatus for determining the angle as a variable for a deviation in the movement from the straight-ahead direction or target direction. In particular, the invention relates to a method and an apparatus for measuring the slip angle.
The slip angle is an important parameter in automotive technology and the development of non-rail-bound land vehicles. In the field of tire development, for example, by this means, conclusions can be drawn regarding the side forces and the running behavior of the tires of a vehicle.
The slip angle in this case is understood to be the angle between the direction in which a tire points and the direction in which it actually moves on the road surface. If, according to this, a tire has a large slip angle, a large lock angle is necessary in order to bring about the desired change of direction. The stiffer the tire construction, the smaller, usually, is the slip angle and the safer is the vehicle handling, although usually at the cost of comfort.
A tire which points straight ahead whilst the vehicle moves evenly straight ahead therefore has a slip angle of 0°; a tire which points 5° to the left whilst the vehicle continues to move straight ahead due, for example, to aquaplaning, has a slip angle of 5°.
Using simultaneous measurement of the slip angle at the front and rear wheels, conclusions can be drawn regarding the drift angle, that is the rotation of the whole vehicle relative to the movement direction.
U.S. Pat. No. 5,371,677 (=DE 40 30 653) describes a method for determining the slip angle of a braked vehicle. In the method described therein, based on a simplified vehicle model and using the wheel speed, the wheel angle, the yaw angle and the main brake cylinder pressure as measured variables, the slip angle is determined as an estimated variable. The method therefore requires a plurality of measured variables that have additionally to be detected or are known. It is not a measurement, but an estimation of the slip angle that is undertaken.